Recently, public attention has been directed to a technique wherein internally gellated resin microparticles are added to an aqueous or a solvent type coating composition to increase the resinous content of the composition without undesired increase in viscosity thereof. However, heretofore proposed resin particles are merely of filler type and can never participate in the film forming. Therefore, the coating formed from such resin particle containing composition was indeed excellent in hardness and abrasion resistance, but was rather incapable of improvement in tensile strength. Thus, it always left something to be desired in heat resistance, water resistance and weathering property of the coating. Under the circumstances it would be of inestimable value of internally gellated resin particles could be obtained which are useful as an additive for a resinous solution and which are capable of resulting, when compounded with a reactive monomer or oligomer, a coating or cured product which is excellent in all respects of hardness, abrasion resistance, tensile strength, heat resistance, water resistance and weathering property. A principal object of the invention is, therefore, to provide such material. An additional object of the invention is to provide a method for the preparation of such resin particles. Further object of the invention is to provide a curable composition containing the same.
Having studied the behavior, in film forming, of resin microparticles themselves, the inventors have found that ethylenically unsaturated bonds carried on the surface of internally gellated resin particles can hardly participate in the film forming reaction, that when a carbon chain is connected to the particulate body resin and an ethylenically unsaturated bond is held at the end portion of said carbon chain, said bond can be easily taken into the film forming reaction, and that the said bond between the particulate body resin and the carbon chain can be easily and advantageously formed by the reaction between an active hydrogen bearing group and an isocyanate group and no adverse effects on film properties are resulted therefrom. On the basis of these important findings, the inventors have succeeded in establishing the invention and providing the present novel, reactive, acrylic resin micro-particles.